Output-voltage variable device

ABSTRACT

An output-voltage variable device utilizing a metal oxide semiconductor field-effect transistor is disclosed. A single pole double throw center off switch whose movable contact arm is connected to the gate of the field-effect transistor has its fixed contacts connected to a positive and negative power supplies, and a non-polarized capacitor is inserted between the gate of the field-effect transistor and ground. When the capacitor is charged with the positive charge, the output voltage derived from the source of the field-effect transistor is increased, but when the capacitor is charged with the negative charge, the output voltage is decreased. When the switch is in a neutral position, a constant output voltage may be maintained.

[ June 10, 1975 OUTPUT-VOLTAGE VARIABLE DEVICE [75] Inventors: Shunzo Oka; Shunji Minami, both of Osaka, Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan 221 Filed: Mar. 12, 1973 21 Appl. No.: 340,347

[30] Foreign Application Priority Data [58] Field of Search 307/239, 247 A, 251, 304, 307/309, 311, 238, 202 R; 340/173 CA; 331/127,130,131

[56] References Cited UNITED STATES PATENTS 3,418,479 12/1968 Schmitt 307/311 X 3,454,787 7/1969 Gelernter.....

12/1970 Ogden 307/251 X 3,566,307 2/1971 Morris 307/251 X 3,569,737 3/1971 Bauer..... 307/251 X 3,571,620 3/1971 Hansen..... 307/304 X 3,582,220 6/1971 Nobusawa..... 307/311 X 3,588,525 6/1971 Hatsukano.... 307/247 A 3,721,832 3/1973 Lee 307/304 X 3,742,261 6/1973 Schneider 307/304 3,751,688 8/1973 Hooghordel 307/247 A Primary ExaminerMichae1 J. Lynch Assistant ExaminerB. P. Davis ABSTRACT An output-voltage variable device utilizing a metal oxide semiconductor field-effect transistor is disclosed. A single pole double throw center off switch whose movable contact arm is connected to the gate of the field-effect transistor has its fixed contacts connected to a positive and negative power supplies, and a non-polarized capacitor is inserted between the gate of the field-effect transistor and ground. When the capacitor is charged with the positive charge, the output voltage derived from the source of the field-effect transistor is increased, but when the capacitor is charged with the negative charge, the output voltage is decreased. When the switch is in a neutral position, a constant output voltage may be maintained.

5 Claims, 22 Drawing Figures 3,889,133 PATENTEDJUII 10 I915 SHEET I30 I33 I32 3,889,133 PATENTEDJUH 10 I915 SHEET 3 PATENTEDJUHIO 1915 ,889,133 SHEET 4 SHEET PATENTEDJUH 10 I975 [III FIG. I?

VOLT-RES. Q Er CONVERTER FIG. l8

VOLT.RES.CONVERTER M/3OI r h l LIGHT EMITT. }PHOTOCONDUC:

ELEMENT {TING ELEMENT t:

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VOLT. RES. CONVERTER j SHEET PATENTEDJUH i 0 1915 FIG. 20

OUTPUT-VOLTAGE VARIABLE DEVICE BACKGROUND OF THE INVENTION The present invention relates generally an outputvoltage variable device and more particularly to an output-voltage variable device utilizing a metal oxide semiconductor field-effect transistor MOS FET.

The conventional output-voltage variable devices are generally variable resistors having mechanical contacts which raise various problems and objections.

SUMMARY OF THE INVENTION One of the objects of the present invention is therefore to provide the so-called contactless output-voltage variable device.

Another object of the present invention is to provide a contactless voltage variable device adapted to be actuated by a low input voltage.

Another object of the present invention is to provide a contactless voltage variable device which is simple in construction but reliable and dependable in operation.

According to the present invention, a single pole double throw center off switch is connected to the gate of a MOS FET and has its fixed contacts connected to positive and negative power supplies, and a nonpolarized capacitor is inserted between the MOS FET and ground. When the movable contact of the switch contacts the positive contact, the capacitor is gradually charged so that the gate voltage is increased. As a result, the source follower output voltage of the MOS FET is gradually increased. When the switch is returned to its neutral position, the output voltage may be maintained at a constant level which in turn is is proportion to the voltage across the capacitor. When the movable contact contacts the negative fixed contact, the charge stored on the capacitor is gradually discharged so that the output voltage is decreased accordingly. When the switch is returned to its neutral position, the output voltage may be maintained at a constant level which is in proportion to the remaining charge on the capacitor.

According to the present invention, when the movable contact of the switch contacts first the positive contact and then the negative contact, the output voltage may be increased and then decreased so that the output-voltage variable device of the present invention may accomplish the same function of the conventional variable resistors. Since the output-voltage variable device of the present invention is not provided with the contacts, the noise due to the contact of the sliding arm with the resistor of the conventional variable resistors may be eliminated and the service life may be remarkably increased. That is, the present invention provides an electronic output-voltage variable device. Furthermore, a plurality of independent circuits may be connected to the output terminal of the voltage variable device of the present invention so that the bias voltage applied to these independent circuits may be varied. When the voltage variable devices are used in the fourchannel stereophonic reproduction systems, the difference between characteristics of variable resistors may be remarkably reduced as compared with the conventional variable resistors.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram of a first embodiment of the present invention;

FIG. 2 is a sectional view thereof taken along the line 2 2 of. FIG. 3;

FIG. 3 is a sectional view taken along the line 3 3 of FIG. 2;

FIG. 4 is a circuit diagram of a second embodiment of the present invention;

FIG. 5 is a front view of a third embodiment of the present invention;

FIG. 6 is a sectional view thereof taken along the line 66ofFIG. 7;

FIG. 7 is a sectional view thereof taken along the line 7, 7 of FIG. 6;

FIG. 8 is a sectional view similar to FIG. 6 illustrating a control shaft being depressed;

FIG. 9 is a circuit diagram of a fourth embodiment of the present invention similar to that shown in FIG. 1;

FIG. 10 is a circuit diagram of a variation thereof similar to that shown in FIG. 4;

FIG. 11 is a perspective view of the fourth embodiment of the present invention;

FIG. 12 is a sectional view taken along the line 12 12 of FIG. 11;

FIG. 13 is a sectional view taken along the line 13 13 of FIG. 11;

FIG. 14 is a sectional view taken along the line 14' 14 of FIG. 11;

FIG. 15 is a sectional view similar to FIG. 13 illustrating one of the pushbuttons being depressed;

FIG. 16 is a circuit diagram of the fifth embodiment;

FIG. 17 is a sectional view of a sixth embodiment of the present invention;

FIG. 18 is a schematic view of a voltage-resistance converter used in the sixth embodiment shown in FIG. 17;

FIG. 19 is a circuit diagram of the sixth embodiment;

FIG. 20 is a front view of a seventh embodiment of the present invention;

FIG. 21 is a sectional view taken along the line 21 21 of FIG. 22; and

FIG. 22 is a sectional view taken along the line 22 22 of FIG. 21.

The same reference numerals are used to designate the same parts throughout the figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment, FIGS. 1, 2, 3

A single pole double throw center off switch Sw has a positive contact 4 and a negative contact 5 which are connected to a power supply, and movable contacts 25 and 26 which are connected through an input resistor 11 to the gate 18a of a MOS FET to which is also connected one terminal of a non-polarized capacitor 19 whose other terminal is grounded. A drain resistor 12 is inserted between a positive DC supply V and the drain 18b of the MOS FET 18, and an output resistor 13 and an output terminal 6 are connected to the source of the MOS FET 18.

Next, the mode of operation will be described. When the movable contact 25 of the switch Sw is connected to the positive contact 4, the capacitor 19 is charged through the input resistor 1 1, and the voltage across the capacitor 19 is applied to the gate 18a of the MOS FET 18 so that the current flows from the drain 18b to the source 180 of the MOS FET. The voltage across the output resistor 13 is derived from the output terminal 6 as an output voltage.

When the movable contact 25 is connected to the positive contact 4, the output voltage is increased as the voltage across the capacitor 19 is increased as long as the MOS FET 18 is not saturated.

When the movable contact 25 is in the center or in a neutral position that is, out of contact with the positive contact 4, the voltage across the capacitor 19 may be maintained as the input resistor 11 has a very large resistance. Therefore, the output voltage may be maintained at a level which is in proportion to the voltage across the capacitor 19.

When the movable contact 26 is connected to the negative contact 5, the charge stored on the capacitor 19 is reduced so that the gate voltage of the MOS FET is reduced. As a result, the output voltage derived from the output terminal 6 is reduced. When the movable contact 26 is connected to contact at a suitable time, the output voltage may be maintained at a level which is in proportion to the remaining voltage across the capacitor 19.

The charging and discharging speeds of the capacitor 19 may be controlled by varying the resistor 11, and the output voltage may be controlled by varying the resistors 12 and 13.

The first embodiment of a device for varying the output voltage, in accordance with the present invention, is shown in FIGS. 2 and 3 in which the component parts similar to those shown in FIG. 1 are designated by the same reference numerals. A casing 1 has an insulating member 2 inverted in a U-shape in cross section fitted into the casing 1 from the bottom thereof, and two knob holes 3 formed through the top of the casing 1. The insulating member 2 is provided with the input terminal 4, the output terminal 5, the bias terminal 7 and the ground terminal 8. A printed-wiring board 9 disposed within the casing l and at the top of the insulating member 2 is provided with the contacts 4a 8a electrically connected through wires 10 to the terminals 4 8, respectively, the resistors 11, 12 and 13 formed by the conventional method, and electrodes 14, l5, l6 and 17 as best shown in FIG. 3. The input resistor 11 is formed between the electrodes l4-and 15; the resistor 12 is formed between the bias contact 7a connected to the bias terminal 7 and the electrode 16; and the resistor 13 is formed between the ground contact 8a connected to the ground terminala 8 and the output contact 6a connected to the output terminal 6. The MOS F ET 18 which is mounted upon the undersurface of the printed-wiring board 9 has its gate, drain and source connected to the electrodes 15 and 16 and the contact 6a, respectively. The capacitor 19 is also mounted on the undersurface of the printed-wiring board 9 and is connected to the electrodes 15 and 17. A retaining member 20 U-shaped in cross section and made of an electrically conductive metal is fitted into the casing 1 and has its lower ends 21 folded back into an inverted U-shape. Holes 22 are formed through the top of the retaining member 20 coaxially of the knob holes 3 of the casing 1, respectively. The retaining member 20 is brought into electrical contact with the electrode 14 upon the printed-wiring board 9. A

switching plate or arm 23 made of an electrically insulating material is pivoted with a pin 24a at its midpoint to a support 24 extending the center of the printedwiring board 9. The movable contacts 25 and 26 comprise L-shaped leaf springs whose lower ends are fitted into and retained in position by the inverted U-shaped lower ends 21 of the retaining member 20 and whose other ends are brought into contact with both ends of the undersurface of the switching plate or arm 23 under a suitable resilient force. The other ends of the leaf spring movable contact arms 25 and 26 are provided with dowels or projections 27 and 28. Each of the pushbuttons 31 and 32 has a stem 29 or 30 extending through the hole 3 of the top of the casing 1 and the hole 22 of the top of the retaining member 20, and an enlarged diameter end or flange 33 or 34 located below the top of the retaining member 20 and immediately above the switching plate or arm 23. A spring 35 or 36 is loaded between a spring seat 37 fitted over the stem 29 or 30 below the head or knob 31 or 32 and the top of the retaining member 20 so that the pushbutton 31 or 32 is normally biased to move upwardly, the flange 33 or 34 normally contacted the undersurface of the top of the retaining member 20, and the head 31 normally extends beyond the top of the casing 1.

Next, the mode of operation will be described. The input terminals 4 and 5 are connected to the positive and negative power sources (not shown) and the bias terminal 7 is connected to the DC power supply V In inoperative condition, the switching plate 23 is maintained horizontally under the force of the leaf springs 25 and 26 so that all of the contacts are not closed. When one of the pushbuttons 31 is depressed against the spring 35, the flange 33 at the lower end of the stem 29 of the pushbutton 31 pushes downwardly the left arm of the switching plate 23 about the pin 24a so that the switching arm 23 rotates about the pin 24a in the counterclockwise direction. As a result, the leaf spring or moving contact arm 25 is bent downwardly so that the dowel or projection 27 at the leading end thereof is connected to the contact 4a connected to the input terminal 4. The capacitor 19 is charged through the input resistor 11, and the voltage across the capacitor 19 is applied to the gate of the MOS FET 18 so that the current flows from the drain to the source thereof. The output voltage is derived from the output terminal 6. As long as the leaf spring or moving contact arm 25 is connected to the contact 42 and the MOS FET 18 is not saturated, the output voltage is in proportion to the voltage charged across the capacitor 19.

When the pushbutton 31 is released, it returns to its initial or neutral position as shown in FIG. 2 under the force of the spring 35 so that the switching plate or arm 23 is returned to its normal horizontal position under the force of the leaf spring or moving contact arm 25 which is moved away from the input contact 42. Therefore, the output voltage is maintained at a constant level which is in proportion to the voltage across the capacitor 19.

When the pushbutton 32 is depressed, the dowel or projection 28 of the leaf spring 26 is connected to the input contact 5a in a manner substantially similar to that described above with reference to the pushbutton 31. Then, the charge stored on the capacitor 19 is reduced so that the output voltage derived from the output terminal 6 is also reduced accordingly. When the pushbutton 32 is released at a suitable time, the switching plate or arm 23 returns to its normal or neutral horizontal position and the leaf spring or moving contact arm 26 is moved away from the input contact 5a. Therefore, the output voltage is also maintained at a constant level which is in proportion to the remaining voltage across the capacitor 19.

When both of the pushbuttons 31 and 32 are depressed, both of the flanges 33 and 34 engage with the switching arm 23 so that the latter is maintained in a horizontal neutral position. Therefore, the leaf springs or moving contact arms 25 and 26 are prevented from contacting the input contacts 4a and 5a simultaneously.

The charging and discharging speeds of the capacitor 19 may be controlled by adjusting the resistor 11, and the output voltage may be controlled by adjusting the resistors 12 and 13.

Second Embodiment, FIG. 4

In FIG. 4 illustrating a circuit diagram of the second embodiment of the present invention, component parts similar to those of the first embodiment shown in FIG. 1 are designated by same reference numerals. The circuit of the second embodiment is substantially similar to that of the first embodiment except that a neon discharge lamp 39 is inserted between the input resistor 11 and a parallel circuit consisting of a capacitor 41 and a resistor 40 is connected to the drain circuit of the MOS FET 18 for stabilizing the output voltage. The second embodiment is adapted to vary the output voltage in the order of 100 volts.

Third Embodiment, FIGS. 5, 6, 7 and 8 As shown in FIG. 5, the device for varying the output voltage in accordance with the present invention, generally comprises a mounting plate 101 securely fitted over a bearing member 103 together with a shielding plate 102, an operating shaft 105 which is vertically slidably and rotatably supported by the bearing member 103, a metal cover 106 U-shaped in cross section as best shown in FIG. 6 and securely fixed to the mounting plate 101 with lugs 107, an upper switch casing 112 inverted U-shaped in cross section as shown in FIG. 6 and having its top securely fixed to the bottom of the cover 106, an insulating plate 114 securely fixed to the opened end of the upper switch casing 112 with lugs 113, and a cylindrical lower switch casing 116 whose upper end is securely fixed to the insulating plate 1 14 with lugs 115 and which has a printed-wiring board 117 fixed to the lower end or bottom thereof.

Next, referring to FIG. 6, a horseshoe shaped resistor 104 is mounted upon the undersurface of the mounting plate 101, and a moving arm or brush 109 which is slidably in contact with the resistor 104 is mounted upon a support or holder 108 located within the casing 106 and made of an insulating material. A contact 110, in contact with the arm 109, is electrically connected to a terminal 111 fixed to the mounting plate 101 for external connection, and two terminals (not shown) are provided at the ends of the resistor 104 for external connection.

The operating shaft 105 extends downwardly through the holes formed through the support or holder 108, the bottom of the cover 106, the tops of the upper switch casing 112 and an insulating member 118 which is similar in shape to the casing 112 and fitted therein, and the insulating plate-1 14 into the lower switch casing 116. A switching plate 119 made of an electrically conductive material is fitted over the operating shaft within the upper switching casing 112 and is securely retained in position by means of washers 120 and 121 which are also fitted over the operating shaft 105. Springs 122 and 123 are fitted over the control shaft between the washer 120 and the top of the insulating member 118 and between the washer 121 and the insulating plate 114.

The top of the insulating member 118 is provided with a stationary contact 124 and a common stationary contact 125 and the insulating plate 114 is provided with an outgoing stationary contact 126 and a common outgoing stationary contact 127 in opposed relation with the contacts 124 and 125, respectively. The contacts 125 and 127 are connected to each other through a lead wire 128. The insulating plate 114 is further provided with a common outgoing stationary contact 148 which is connected to the contact 124 through a lead wire 129.

The printed-wiring board 117 is provided with two input terminals 130 and 131, an output terminal 132, a bias terminal 133, a ground terminal 134 and electrodes 138 141. A resistor 135 is formed between the electrodes 138 and 139, a resistor 136 between the bias terminal 133 and the electrode 140, and a resistor 137 between the output terminal 132 and the earth terminal 134. The contact 127 on the insulating plate 114 is connected through a lead wire 142 to the electrode 138, and the contacts 126 and 148 are also connected to the input terminals 130 and 131 through lead wires 143 and 144, respectively. A MOS field-effect transistor whose source is connected to the output terminal 132 and a non-polarized capacitor 145 which is electrically inserted between the electrodes 139 and 141 are mounted on the printed-wiring board 117 within the lower casing 116.

Next, the mode of operation will be described with further reference to FIG. 9. The input terminals 130 and 131 are connected to positive and negative power supplies (not shown) respectively, and the bias terminal 133 is connected to the DC supply V In the inoperative mode, the switching plate 119 is positioned at the center of the upper switching case 112 as shown in FIG. 6 and moved away from the contacts 124, 125, 126 and 127.

When the operating shaft 105 is depressed, as shown in FIG. 8, against the springs 122 and 123, the switching plate 119 is connected to both the contacts 126 and 127 so that the input terminal 130 is connected to the electrode 138 on the printed-wiring board 117 through the lead wires 142 and 143 and the switching plate 1 19. The capacitor 146 is charged through the input resistor 135, and the voltage across the capacitor 146 is applied to the gate of the MOS FET 145 so that the current flows from the drain to the source thereof. The output voltage across the resistor 137 is derived from the output terminal 132. As long as the switching plate or moving contact arm 119 makes contact with both the contacts 126 and 127 and'the MOS FET is not saturated, the output voltage is increased in proportion to the voltage across the capacitor 146.

When the operating shaft 105 is released, it is returned to its initial position shown in FIG. 6 under the force of the spring 123, and the output voltage is maintained at a constant level which is in proportion to the existing voltage across the capacitor 146.

' voltage derived from the output terminal 132 is decreased accordingly. When the control shaft 105 is returned to its initial or neutral position at a suitable time, the output voltage is maintained at a constant level which is in proportion to the voltage across the capacitor 146.

The charging and discharging speeds of the capacitor 146 may be controlled by adjusting the resistor 135, and the output voltage may be controlled by adjusting the resistors 136 and 137.

When the control shaft 105 is rotated while it is in neutral position or its switching plate or movable contact arm 119 closes the contacts 126 and 127 or the contacts 124 and 125, the arm or brush 109 slides over the resistor 104 so that the resistance between the terminal 11 1 and the terminals at both ends of the resistor 104 may be varied. Thus, the device for varying the output voltage of the third embodiment, in accordance with the present invention, is adapted not only to control the volume but also to attain a balance between the two channels or control the tone.

As a variation of the fourth embodiment, an electrical circuit shown in FIG. and similar to that shown in FIG. 4 may be incorporated instead of the circuit shown in FIG. 9.

Fifth Embodiment, FIGS. 11 16 The fifth embodiment of the present invention shown in FIGS. 11 16 is substantially similar in construction and operation to the first embodiment described with reference to FIGS. 1, 2 and 3 except that a voltmeter 234 is mounted upon the top of a casing 201 and is connected between an output terminal 206 and a ground terminal 208 in order to facilitate the control of the output voltage and to permit the reading of the controlled voltage.

Referring to FIGS. 11 15, a casing 201 has a printed-wiring board 202 fitted to the bottom thereof and holes 203 formed through the top thereof for receiving pushbuttons 226 and 227, respectively. The printedwiring board 202 is provided with an input terminal 204, an output terminal 206, a bias terminal 207 and a ground terminal 208. The printed-wiring board 202 is further provided with resistors 209 211 formed by any conventional technique and electrodes 212 215. The resistor 209 is formed between the electrodes 212 and 213; the resistor 210, between the bias terminal 207 and the electrode 214; and the resistor 211, between the output terminal 206 and the ground terminal 208, A MOS field-effect transistor 216 is mounted upon the printed-wiring board 202 and has its gate connected to the electrode 213, its drain connected to the electrode 214 and its source to the output terminal 206, and a non-polarized capacitor 217 is also mounted upon the printed-wiring board 202 within the casing 201 and inserted between the electrodes 213 and 215.

A support 218 made of a metal and inverted U- shaped in cross section is fitted into the casing 201 in such a manner that its lower end is connected to the printed-wiring board 202. The support 218 has two holes formed through the top thereof in opposed and coaxial relation with the pushbutton holes 203 formed through the top of the casing 201. A switching arm 219 has its midpoint pivoted with a pivot 220a to a support 220 extending from the center of the printed-wiring board 202. Each of L-shaped leaf springs or movable contacts 221 and 222 has its lower end securely fixed to the printed-wiring board 202 and the leaf spring or movable contact arm 221 has its lower end and con nected electrically to the electrode 212 with a lead wire 223. The other ends of the L-shaped leaf springs or movable contacts 221 and 222 are engaged with the switching plate or arm 219 with a suitable upward biasing force and are also electrically connected thereto.

Each of the pushbuttons 226 and 227 comprises a head, a stem 224 or 225 extending through the holes formed through the tops of the casing 201 and the support 218 and a large-diameter portion or flange 228 or 229 formed at the lower end thereof and normally located below the top of the support 218 and immediately above the switching arm 219. A spring 230 or 231 is fitted over the stem 224 or 225 between the top of the support 218 and a spring seat 232 or 233 fitted over the stem 224 or 225 closer to the head 226 or 227. Therefore, the pushbuttons 226 and 227 are normally biased to move upwardly and their flanges 228 and 229 contact the undersurface of the top of the support 218.

As the mode of operation of the fifth embodiment with the above construction is substantially similar to that of the first embodiment described in detail with reference to FIGS. 1, 2 and 3, no description will be provided in this specification except that the output voltage is indicated by the voltmeter 234.

Sixth Embodiment, FIGS. 17, 18 and 19 The sixth embodiment shown in FIGS. 17 19 is substantially similar in construction and operation to the fifth embodiment described with reference to FIGS. 1 1 16 except that instead of the voltmeter 234, a voltageresistance converter 301 having a pair of output terminals 302 and 303 is connected across the output and ground terminals 206 and 208. As shown in FIG. 18, the voltage-resistance converter generally indicated by 301 comprises a light emitting element 304 such as a lamp, an electroluminescent diode, or the like and a photoconductive cell 305, disposed to receive the light emitted from the element 304. The voltage-resistance converter 301 is light-tightly sealed so that light from the exterior will not impinge upon the photoconductive cell 305. The light emitting element 304 is connected between the output terminal 206 and the electrode 215 and hence the ground terminal 208.

The intensity of light emitted from the light emitting element 304 varies depending upon the voltage across the resistor 211 so that the resistance of the photoconductive element 305 is varied accordingly and is derived from the pair of output terminals 302 and 303. Opposed to the embodiments described above, the sixth embodiment is characterized in that its output is a resistance instead of a voltage.

Seventh Embodiment, FIGS. 20 22 The seventh embodiment shown in FIGS. 20, 21 and 22 is similar to the second embodiment described above with reference to FIGS. 5 9 except that it furating shaft 405 independently of the variable resistor 435 as will be described in more detail hereinafter.

A mounting plate 401 which is securely fitted over a 403 fixed to the undersurface thereof. The bearing member 402 is adapted to rotatably support the outer control shaft 404, and the inner operating shaft 405 is rotatably and vertically slidably supported by the outer control shaft 404. A cap shaped cover 406 made of a metal is securely fixed to the mounting plate 401 with lugs 407, and a movable arm or brush 409 which is adapted to slide over the resistor 403 is supported by a support 408 which is made of an insulating material and is securely fitted over the outer control shaft 405 within the cover 406. A contact 410 which is normally in contact with the arm or brush 409 is electrically connected to a terminal 411 for external connection. The ends of the resistor 403 are connected to terminals (not shown) attached to the mounting plate 401 for external connection.

An intermediate bearing member 412 extending through the bottom of the cover 406 supports the outer control shaft 405 and is fitted with a mounting plate 414 of the second variable resistor 436 and a shielding plate 414 which provides shielding between the first and second variable resistors 435 and 436.

A horseshoe-shaped resistor 415 is mounted upon the undersurface of the mounting plate 414 and has both of its ends connected to terminals (not shown) on the mounting plate 141 for external connection. The arrangement of a movable arm or brush 420, its contact 416 and terminal 417, a casing or cap made of a metal 418, and a support 419 for the movable arm or brush 420 is similar to that of the first variable resistor 435 described above.

A spacer 421 is fitted over the outer control shaft 405 between the arm or brush support 419 and an intermediate bearing member 422 over which are fitted a mounting plate 424 of the third variable resistor 437 and a shield plate 423 which prrovides shielding between the second and third variable resistors 436 and 437.

The third variable resistor 437 further comprises a cap or casing 428, a resistor 425, its movable arm or brush 430 contact 426, terminal 427, and support 429 and a spacer 431, all of which are arranged in a manner substantially similar to that described with reference to the second variable resistor 436.

To an intermediate bearing 432 is fixed a mounting plate 434 of a variable output voltage device and a shield plate 433 which provides shielding between the third variable resistor 437 and the variable output voltage device.

As described above, the first variable resistor 435 is adjusted by the rotation of the outer control shaft 404, and the second and third variable resistors 436 and 437 are adjusted by the rotation of the inner control shaft 405. i

An upper switch casing 438 is securely fixed to the mounting plate 434 with lugs 439 and has an insulating bearing member 402 has a horseshoe-shaped resistor plate 440 fixed to the lower end thereof. A lower switch casing 442 is securely fixed to the insulating plate 440 with lugs 441 and has a printed-wiring board 443 securely fixed to the lower end thereof with lugs 444.

The inner control shaft 405 extends through the in termediate bearings 412, 122 and 432, the spacers 421 and 431 and a bearing member 445 fixed to the insulating plate 440 between the upper and lower switch casings 438 and 442 into the lower switch casing 442. A switching plate or arm 446 made of an electrically conductive material is securely fixed over the inner control shaft 405 in the upper switch casing 438 and is retained in position between a pair of upper and lower washers 447 and 448 which are also fitted over the inner control shaft 405. Springs 449 and 450 are fitted over the inner control shaft 405 between the intermediate bearing member 432 and the upper washer 447 and between the lower washer 448 and the bearing member 445. The mounting plate 434 is provided with a fixed contact 451 and a common fixed contact 452, and the insulating plate 440 is provided with an outgoing fixed contact 453 and a common outgoing fixed contact 454.

- The contacts 452 and 454 are electrically interconnected with a lead wire 455, and these contacts 451 and 452 on the mounting plate 434 and the contacts 453 and 454 on the insulating plate 440 are located in opposed relation to each other. The insulating plate 440 is further provided with a fixed contact 456 which is electrically connected to the contact 451 on the mounting plate 434 through a lead wire 457.

The printed-wiring board 443 is provided with input terminals 458 and 459, an output terminal 460, a bias terminal 461, a ground terminal 462, resistors 463 465 and electrodes 460 465 formed by a suitable printed-wiring technique. The resistor 463 is formed between the electrodes 466 and 467; the resistor 464, between the bias terminal 461 and the electrode 468; and the resistor 465, between the output and ground terminals 460 and 462. The contacts 453, 454 and 456 on the insulating plate 440 are connected to the input terminals 458 and 459 and the electrode 466 through lead wires 471, 472 and 470, respectively. A MOS FET 473 is mounted upon the printed-wiring board 443 and has its gate connected to the electrode 467, its drain to the electrode 468 and its source to the output terminal 460. A non-polarized capacitor 474 on the printedwiring board 443 is electrically inserted between the electrodes 467 and 469.

Next, the mode of operation will be described, but 7 the mode of operation of the variable output voltage device is substantially similar to that of the sixth embodiment described above so that no description will be set out therefor in this specification. When the inner control shaft 405 is rotated the arms or brushes 420 and 430 slide over the resistors 415 and 425 so that the resistances between the movable arm or brush and the terminals of the resistors may be varied. That is, the variable resistors 436 and 437 may be simultaneously controlled. In this case, the inner control shaft 405 is rotated so that the switching arm 446 may be in the neutral position, but it may be also rotated while the switching arm 446 closes the contacts 451 and 452 or 453 and 454. Therefore, the seventh embodiment can control the volume by the variable output voltage device, attain a balance between the two sound channels and control the tone.

What is claimed is:

1. An output-voltage variable device comprising a. a metal oxide semiconductor field-effect transistor having a gate, a drain and a source,

b. an input resistor, a neon discharge lamp connected in series with the input resistor, a single-pole double-throw center-off switch having a movable contact arm connected through said input resistor and said neon discharge lamp to the gate of said field-effect transistor and having fixed positive and negative contacts connected to positive and negative DC sources, respectively, and connected to said movable contact arm by operative movement of said arm,

0. a non-polarized capacitor connected between said gate of said field-effect transistor and ground,

d. a drain resistor connected between the drain of said field-effect transistor and a positive DC sup- P y e. an output resistor connected between the source of said field-effect transistor and ground,

f. an output terminal connected to said output resistor for deriving an output voltage whereby movement of said movable contact arm from the positive to the negative source and from the negative source to the positive source gradually charges and discharges said non-polarized capacitor, the output voltage thereby following the voltage on said nonpolarized capacitor,

g. a casing for housing therein said MOS field-effect transistor, said input resistor, said switch, said capacitor, said drain resistor and said output resistor, said casing being provided with a positive input terminal electrically connected to said positive contact of said switch, a negative terminal electrically connected to said negative contact, a bias terminal electrically connected to said drain resistor, an output terminal electrically connected to said source of said field-effect transistor, and a ground terminal electrically connected to the grounding end of said capacitor and said output resistor, all of said terminals of said casing being used for external connections to said positive and negative DC sources, said bias DC supply, and ground,

h. an operating shaft drivingly connected to said movable contact arm, and

i. a variable resistor mechanically connected to said shaft, said variable resistor being adjusted simultaneously with the actuation of said single-pole double-throw center-off switch.

2. A device as defined in claim 1, further comprising a second operating shaft coaxially and rotatably mounted on said first operating shaft, and a plurality of additional variable resistors drivingly coupled to said second operating shaft.

3. An output voltage variable device comprising a. a metal oxide semiconductor field-effect transistor,

having a gate, a drain and a source,

b. an input resistor, a neon discharge lamp connected in series with the input resistor, a switch having a movable contact arm connected through said input resistor and said neon discharge lamp to the gate of said field-effect transistor, and having fixed positive and negative contacts connected to positive and negative DC sources, respectively, and connected to said movable contact arm by operative movement of said arm,

c. a non-polarized capacitor connected between said gate of said field-effect transistor and ground,

d, a drain resistor connected between the drain of said field-effect transistor and a positive DC sup- P y e. an output resistor connected between the source of said field-effect transistor and ground,

f. an output terminal connected to said output resistor for deriving an output voltage whereby move ment of said movable contact arm from the positive to the negative source and from the negative source to the positive source gradually charges and discharges said non-polarized capacitor, the output voltage thereby following the voltage on said nonpolarized capacitor, and

g. the voltage-resistor converter means connected to the output terminal of the device for changing the output voltage to a corresponding resistance, said converter comprising a light-emitting element means for converting said output voltage into light, and a photo-conductive cell having an output terminal and adapted to receive light emitted from said light-emitting element, whereby at the output terminal of said photo-conductive cell a resistance corresponding to the voltage across said nonpolarized capacitor is obtained.

4. A device as defined in claim 3, wherein said switch is a single-pole double-throw center off switch, further comprising a casing for housing therein said MOS fieldeffect transistor, said input resistor, said switch, said capacitor, said drain resistor and said output resistor, said casing provided with a positive input terminal electrically connected to said positive contact of said switch, a negative terminal electrically connected to said negative contact, a bias terminal electrically connected to said drain resistor, an output terminal electrically connected to said source of said field-effect transistor, and a ground terminal electrically connected to the grounding ends of said capacitor and said output resistor, all of said terminals of said casing being used for external connections to said positive and negative DC sources, said bias DC supply, and ground,

said casing further having therein a variable resistor drivingly coupled to said movable contact arm, and a variable resistor drivingly coupled to said operating shaft, whereby the single-pole double-throw center-off switch may be adjusted simultaneously with the adjustment of said variable resistor.

5. A device as defined in claim 1, further comprising a second operating shaft coaxially and rotatably mounted on said first operating shaft, and a plurality of additional variable resistors drivingly coupled to the 

1. An output-voltage variable device comprising a. a metal oxide semiconductor field-effect transistor having a gate, a drain and a source, b. an input resistor, a neon discharge lamp connected in series with the input resistor, a single-pole double-throw center-off switch having a movable contact arm connected through said input resistor and said neon discharge lamp to the gate of said field-effect transistor and having fixed positive and negative contacts connected to positive and negative DC sources, respectively, and connected to said movable contact arm by operative movement of said arm, c. a non-polarized capacitor connected between said gate of said field-effect transistor and ground, d. a drain resistor connected between the drain of said fieldeffect transistor and a positive DC supply, e. an output resistor connected between the source of said field-effect transistor and ground, f. an output terminal connected to said output resistor for deriving an output voltage whereby movement of said movable contact arm from the positive to the negative source and from the negative source to the positive source gradually charges and discharges said non-polarized capacitor, the output voltage thereby following the voltage on said non-polarized capacitor, g. a casing for housing therein said MOS field-effect transistor, said input resistor, said switch, said capacitor, said drain resistor and said output resistor, said casing being provided with a positive input terminal electrically connected to said positive contact of said switch, a negative terminal electrically connected to said negative contact, a bias terminal electrically connected to said drain resistor, an output terminal electrically connected to said source of said field-effect transistor, and a ground terminal electrically connected to the grounding end of said capacitor and said output resistor, all of said terminals of said casing being used for external connections to said positive and negative DC sources, said bias DC supply, and ground, h. an operating shaft drivingly connected to said movable contact arm, and i. a variable resistor mechanically connected to said shaft, said variable resistor being adjusted simultaneously with the actuation of said single-pole double-throw center-off switch.
 2. A device as defined in claim 1, further comprising a second operating shaft coaxially and rotatably mounted on said first operating shaft, and a plurality of additional variable resistors drivingly coupled to said second operating shaft.
 3. An output voltage variable device comprising a. a metal oxide semiconductor field-effect transistor, having a gate, a drain and a source, b. an input resistor, a neon discharge lamp connected in series with the input resistor, a switch having a movable contact arm connected through said input resistor and said neon discharge lamp to the gate of said field-effect transistor, and having fixed positive and negative contacts connected to positive and negative DC sources, respectively, and connected to said movable contact arm by operative movement of said arm, c. a non-polarized capacitor connected between said gate of said field-effect transistor and ground, d. a drain resistor connected between the drain of said field-effect transistor and a positive DC supply, e. an output resistor connected between the source of said field-effect transistor and ground, f. an output terminal connected to said output resistor for deriving an output voltage whereby movement of said movable contact arm from the positive to the negative source and from the negative source to the positive source gradually charges and discharges said non-polarized capacitor, the output voltage thereby following the voltage on said non-polarized capacitor, and g. the voltage-resistor converter means connected to the output terminal of the device for changing the output voltage to a corresponding resistance, said converter comprising a light-emitting element means for converting said output voltage into light, and a photo-conductive cell having an output terminal and adapted to receive light emitted from said light-emitting element, whereby at the output terminal of said photo-conductive cell a resistance corresponding to the voltage across said non-polarized capacitor is obtained.
 4. A device as defined in claim 3, wherein said switch is a single-pole double-throw center-off switch, further comprising a casing for housing thereIn said MOS field-effect transistor, said input resistor, said switch, said capacitor, said drain resistor and said output resistor, said casing provided with a positive input terminal electrically connected to said positive contact of said switch, a negative terminal electrically connected to said negative contact, a bias terminal electrically connected to said drain resistor, an output terminal electrically connected to said source of said field-effect transistor, and a ground terminal electrically connected to the grounding ends of said capacitor and said output resistor, all of said terminals of said casing being used for external connections to said positive and negative DC sources, said bias DC supply, and ground, said casing further having therein a variable resistor drivingly coupled to said movable contact arm, and a variable resistor drivingly coupled to said operating shaft, whereby the single-pole double-throw center-off switch may be adjusted simultaneously with the adjustment of said variable resistor.
 5. A device as defined in claim 4, further comprising a second operating shaft coaxially and rotatably mounted on said first operating shaft, and a plurality of additional variable resistors drivingly coupled to the second operating shaft. 